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THE AMERICAN NATURALIST [Vol. XLI 



theory of descent with modification, the exact genealogical relation- 

 slii{) of animals has been an ever recurring cjuestion. In one way 

 or another it seems to have fascinated c(^rtain workers. AVith the 

 superficial, it takes the form of arrangements of living sj)ecies in what 

 is assumed to be a genealogical sequence without regard to the fact 

 that these animals are of the same generation, so to sjx-ak, and not 

 ancestrally r(>lat(>d. Speculations of this kind have brought nnich of 

 tills work into (lisrej)ute. With the serious-minded, attempts have 

 b(-( 11 made to asccMMain the principles by which kinship among ani- 

 mals can be determined, and to this class belongs the volume under 

 consideration. 



With much care and erudition :\rontgom.-r> h..s .o,:ol); for a sound 

 basis by which animal relationship can be asccriaiiird. 'Tins he has 

 formulated in a series of i.rincii)les as follows: (irst, evidence of kin- 

 ship must be sought in tlie pliysioloijical as well as the morphological 

 relations of animals, for iliese iw, i.rovinces are in reality mutually 

 interdependent; secon<ll\-, all the laeiors concerning animal processes 

 must be scrutinized; thinlly, the relative value of the different kinds 

 of evidence must be considered; fourthly, monophyletic origins should 

 be assumed unless the opposite can be proved; fifthly, ai)proximately 

 intermediate connectants between species should be anticij)rit(>d; 



It is noteworthy that two clasps of evidcn.-e imieli in vogue in the 

 discussion of questions of this kind are heliitled by ?^Ionigoinery. 

 According to him no special liglii is throw n l)y embryology on phy- 



reeapiinlale the devcloj )nieni of ilu> race; and the evidence brought 



